In many industries such as medical, electronic assembly, tool, and fixturing industries, there are circumstances when a limited amount of torque should be applied to mechanical devices, such as fasteners. As one example when using bone penetrating pins especially for attachment of halos or like mechanical appliances, it is necessary to limit the amount of torque applied to the fastener (such as described generally in U.S. Pat. No. 4,838,264, the disclosure of which is hereby incorporated by reference herein). It is desirable to be able to provide such torque limited applicators at low cost, and in some industriesxe2x80x94such as the medical industryxe2x80x94low enough cost so that they are disposable. Sometimes single use breakaway types of torque limited applicators are used, but in some situations it is desirable to be able to have a reusable torque limited applicator, e.g. one that can at least be used with a plurality of fasteners, the number of fasteners being suitable to at least perform a particular procedure.
The torque limited applicator according to the present invention is simple and easy to construct, having a minimum number of components, wide diversity in component configurations that allows great flexibility depending upon the particular industry and particular mechanical devices (such as fasteners) to be utilized therewith, and being constructable of a wide variety of materials. Typically the torque limited applicator includes at least a torque applying element and a fastener drive structure, one of the components having cam followers and the other a cam element which cooperates with each other so that the torque applying element drives the fastener drive structure until a predetermined torque is reached, at which point there is relative rotational movement between the cam followers and the cam element. The cam element can have any number of xe2x80x9clobesxe2x80x9d and any suitable configuration, and two or more cam followers may be provided. Both components may be formed of an integral piece of plastic, e.g. by injection molding, or by milling, turning, or other machining.
In most circumstances it would be desirable to have the torque applying element and the fastener drive structure connected together so that they do not separate during normal use. This may be provided by using a retaining ring which cooperates with a deformable pin of the fastener drive structure. Also a plug may be utilized to prevent tampering with the internal components, to provide a tamper evident seal, and to prevent the entry of foreign material into the operative area between the cam element and cam followers, as well as to provide an area for the placement of indicia (such as the amount of torque that such an applicator may apply). The plug and retainer ring also can each be an integral piece of plastic.
According to one aspect of the present invention a torque limited applicator is provided comprising the following components: A torque applying element having a tubular body and a handle, the tubular body comprising at least two internal cam followers. A fastener drive structure having first and second ends, and comprising a drive element adjacent the first end, and a cam element adjacent the second end. And, the cam followers and the cam element engaging and cooperating with each other so that upon application of a force to the handle up to a predetermined maximum torque the cam followers engage the cam element to transmit rotational force from the handle to the drive element, and upon the predetermined maximum torque being exceeded the cam followers being deformed and moved past the cam element so that a torque greater than the predetermined maximum cannot be applied to the drive element by the torque applying element.
The cam element may comprise a cylindrical element having a cross-section in the shape of a pointed end ellipse, or may have a wide variety of other dual or multi-lobed configurations.
In one embodiment the tubular body of the torque applicator has an interior surface; and wherein the cam followers comprise at least two oppositely disposed first and second arms of bendable material and each having a contoured surface free end extending outwardly from the interior surface and engaging the cam element; and wherein there is sufficient clearance within the tubular body of the torque applying element between the cam element and the contoured surface free ends so that the free ends may move between the cam element and the tubular body interior along substantially 360E.
The torque applying element and fastener drive structure may each be one integral piece of plastic, and a retaining ring may be provided for connecting the torque applying element and fastener drive structure together so that they are connected during normal use. That is the torque limited applicator cam followers may each comprise a top surface, and further comprise a retaining ring having a central opening therein, the retaining ring having a bottom surface in engagement with the top surface; and the fastener drive structure may include a pin integral therewith and extending upwardly therefrom, the pin having cross-sectional dimensions less than the cross-sectional dimensions of the ring opening, and having a length greater than the thickness of the ring so that a portion of the pin extends above the ring, the portion of the pin above the ring deformed into contact with the top surface of the ring to hold the ring in place.
There also may be bearing surfaces between the torque applying element and the fastener drive structure to facilitate relative rotation therebetween.
The torque limited applicator may also comprise a plug that plugs the torque applying element tubular body at the handle. The plug may have indicia thereon, visible from the exterior of the torque applying element, indicating the predetermined maximum torque that can be applied by the torque applying element. The plug and the retaining ring may also each be one integral piece of plastic, and all of the components can be made of the same plastic, although they can be made of different plastics too (e.g. such as the torque applying element of acetal and the fastener drive structure of polytetrafluoroethylene). Suitable plastics that may be used for the components include acetal (e.g. DELRIN7 500 from DuPont), PBT, PET, polytetrafluoroethylene, polyamide, polycarbonate, polysulfone, PEEK, PEKEKK, and polyetherimide.
At least three torque limited applicators may be utilized, each of the applicators having a different maximum torque and of a different color. All of the components can be of a different color from one torque level to the next, or just the plugs within any given torque level may be of the same color.
The invention also relates to a method of securing a fastener in place, which fastener should be subjected to only a predetermined amount of torque, comprising the steps of (a) selecting an appropriate torque level limited applicator such as described above; (b) bringing the drive element associated with the torque limited applicator into operative contact with a fastener; (c) rotating the torque applying element to drive the fastener drive structure until the desired torque level has been reached as indicated by a tactile or audible indication once the cam followers have moved past the cam element; (d) removing the torque limited applicator from the fastener; and (e) repeating steps (a) through (d) for a second fastener using the same torque limited applicator.
It is the primary object of the present invention to provide a low cost reusable torque limiting device and method of utilization thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.